The present invention relates generally to signal error reduction in positioning systems such as the Global Positioning System (GPS), Global Navigation Satellite system (GLONASS), terrestrial or aircraft based pseudolytes, and the like, and more specifically to a method and apparatus for mitigating multipath signal distortion using a multi-element antenna array.
A significant cause of error in navigation/positioning systems is signal multipath propagation or multipath. Multipath is the interference caused by reflected positioning system signals arriving at the receiver, typically because of nearby structures or other reflective surfaces. For instance, in an aircraft environment, a positioning system signal may be reflected from various structural components of the aircraft fuselage. These reflected elements are received by the positioning system receiver along the desired direct path signal. The reflected signals may differ from the direct path signal in delay, amplitude, and phase, causing signal distortion and, consequently, positioning and navigation errors.
If the path of the reflected signal is considerably longer than the direct path such that the two patterns of signals can be separated, then the multipath effect can be substantially reduced by signal processing techniques. However, in-chip multipath cannot be easily distinguished from the direct path. Partial correlation with one or more multipath signals in addition to the desired, or direct, signal causes the correlation peak to shift leading to pseudorange error and thus signal distortion.
Consequently, it would be advantageous to provide a method and apparatus for mitigating multipath signal distortion in positioning systems such as the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), terrestrial or aircraft based pseudolytes, or the like.
Accordingly, the present invention is directed to a method and apparatus for mitigating multipath signal distortion in navigation/positioning systems such as the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), terrestrial or aircraft based pseudolytes, and the like, using a multi-element antenna array. The multi-element antenna array is used to discriminate between the directed signal and its multipath components based on spatial angle of arrival. A reference signal, provided by the positioning system receiver, is used to compute element weightings that are utilized to null out the multipath components before they reach the receiver.
In accordance with one aspect of the invention, a system for mitigating multipath distortion in a navigation/positioning system signal is described. In an exemplary embodiment, the system comprises a multi-element antenna array capable of receiving a positioning system signal including a direct path component and at least one multipath component. The multi-element antenna array includes at least three antenna elements wherein each antenna element yields an element path signal based on the received positioning system signal. A signal processing section is coupled to the multi-element antenna array. The signal processing section is capable of multiplying each element path signal by a complex weight and summing the weighted element path signals for generating an antenna pattern, each antenna pattern corresponding to a positioning system signal source. In exemplary embodiments of the invention, the system may be implemented as the antenna and radio frequency (RF) section of the navigation/positioning system receiver.
In accordance with a further aspect of the invention, a method for mitigating multipath distortion in a navigation/positioning system signal is described. In an exemplary embodiment the method comprises the steps of receiving a positioning system signal including a direct path component and at least one multipath component utilizing a multi-element antenna having at least three antenna elements wherein each antenna element yields an element path signal based on the received positioning system signal, multiplying each element path signal by a complex weight, and summing the weighted element path signals for generating an antenna pattern wherein each antenna pattern corresponds to a positioning system signal source.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principle of the invention.